Thermal devices for temperature control of food can be divided into three main groups according to their functional purpose:
- devices intended for keeping food in a hot state;
- devices intended for the sale of food;
- devices that combine the above functions and are capable of transporting hot food from the place of storage or preparation to the sales area.
The latter direction is the most promising, since reloading operations are excluded, which not only creates certain organizational conveniences, but also reduces the mass and heat losses that inevitably occur in this case.
In principle, it is possible to store finished culinary products in the main thermal apparatus intended for culinary heat treatment: cooking boilers, steam chambers, etc. To do this, use the lower stages of thermal power, which provide the temperatures necessary for storage. It is obvious that the use of basic thermal apparatus for food storage is not economically feasible, since the cost of this type of equipment is high.
The currently most common hot food storage devices at domestic catering establishments include: food warmers, heat racks, thermostats and heat cabinets.
Food warmers. These are thermal devices designed to store food in a hot state during its sale on the distribution line. The design feature of food warmers, which distinguishes them from other thermostatic devices, is that the food is placed on the stove or in functional containers, or in special containers that are part of the food warmer - food warmers, and the food warmer itself is, as a rule, stationary. Food storage containers are not thermally insulated and can be separated from the food warmer and used not only for storing finished products, but also for cooking them.
Since food warmers are also intended for sale, i.e. are installed in the distribution line, they are, as a rule, sectional modulated devices. At the same time, the area for placing food warmers is most often the plane corresponding to the surface of the desktop and located at a distance of 800...900 mm from the floor level. In some cases, when there is thermostatic control of large volume cookware (20 dm 3 or more), the surface of the compensation heaters on which the containers are installed is located at a distance of 20 ... working conditions of service personnel.
The tabletop scheme is usually used in food warmers designed for temperature control of first courses and side dishes (potato tore, cereals and pasta). This scheme provides for a set of food warmers for all types of culinary products. In the process of storage, as needed, hot food is removed from the food warmers to complete the dishes and sell them. Empty food warmers are replaced with filled ones.
When heating the food warmers with a water bath by changing the power of the heating elements (or the steam flow in the tubular steam exchanger), the temperature of the heating water is reached from 70 to 90 °C. In this case, water vaporization is practically absent. When using a steam bath, the heating steam has a temperature equal to the boiling point.
Food warmers with a water bath, despite the possibility of regulating the temperature of the heating medium, due to their significant mass and large thermal inertia, are inferior in efficiency to analogues with steam heating; for this reason, the latter find much wider application in practice.
The design of bain-marie with air heating of bain-marie is similar to the design of bain-marie with a water bath, but in the heating volume instead of water there is hot air; the heating volume in this case is significantly reduced.
Food warmers with a floor heating surface are most often an electric stove with burners that heat the bottom of the cookware, in which food is thermostated.
Heat racks. These are devices designed to heat dishes (plates, cups, glasses) and portioned and prepared dishes placed in it.
As the main thermal elements, horizontal surfaces (shelves) heated to temperatures of 60 ... 90 ° C are used. In electric heat racks, electric heaters of a closed type are more often used as a heater, operating in the mode of low specific heat loads (W< 2 Вт/см 2).
When using a centralized heat supply scheme for the working surfaces of heat racks, in addition to electric heating, gas or steam heating can be used. In this case, the intermediate heat carrier is heated in the steam generator and pumped through a group of flat heat exchangers by a gear pump. As it moves, the coolant temperature changes from 85...90°C at the inlet to the first group of heat exchangers to 60...70°C at the tail sections. These regime characteristics meet the requirements of food temperature control and, in turn, are the initial ones for determining the power of the apparatus, as well as the power and performance of the gear pump. As an intermediate coolant, either heavy mineral (motor) oil or organosilicon liquids (polyorganosiloxanes) are used.
Thermostats. Thermal devices designed for long-term storage of food at a constant temperature are called thermostats.
A distinctive design feature of thermostats is that the working chamber (temperature control volume) is an integral and completely thermally insulated part of the entire apparatus. Directly in this chamber is food intended for storage.
The main part of the thermostat is a working chamber of a cylindrical shape, or made in the form of a parallelepiped. The loading opening of the working chamber is tightly closed with a lid. To seal the junction, a gasket made of heat-resistant food rubber is usually used. To press the lid, various kinds of mechanical devices are used, more often screw or cam.
Depending on the capacity and method of transportation, thermostats are divided into mobile, portable and stationary.
Portable ones are designed not only for storing and transporting hot food within the enterprise, but also for transporting it by transport. For intrashop movements, mobile thermostats are used, and stationary ones are usually installed in the line of assembly and sale of finished products.
Currently, foreign firms produce various thermostats (from simple portable to combined carts), made of heat-resistant plastic and filled with thermal insulation. Their practical use is constantly increasing.
Electric thermostats are widely used for heating and keeping hot coffee, cocoa, milk and other drinks in the process of their implementation. They are installed on buffet counters, cafeteria counters and in self-service lines. Structurally, they are boilers with direct heating, in which the heating element is located in the lower part of the cooking vessel.
To ensure soft heating of drinks placed in an electric thermostat, it is advisable to use oil heating elements, rather than water ones. In this case, the specific surface power of the heating element tube is reduced from 10 to 6 W/cm2, which significantly reduces the degree of destruction of drinks, especially when they are reheated.
Thermal cabinets. Heating cabinets are a simplified version of fryers and, unlike them, either lack heating elements or are equipped with low-power heaters. The complete absence of heaters is justified in cases where the heating cabinet is an auxiliary part of the main apparatus (hot oven, stove or heat rack) and utilizes the heat generated by this apparatus. Thermal cabinets are used to store individual components of portioned dishes in a hot state. The main structural element of the heating cabinet is a box-shaped working chamber, in the lower part of which, if necessary, heating elements are installed. The stored food product is placed on special shelves or in special boxes. In the first case, the working chamber has a common door, and in the second case, the drawers are pulled out independently of one another.
Heating cabinets of large volumes usually have a power regulator and a thermostat.
The thermostatic devices discussed above operate on electric heating. This is due to the fact that the devices are most often mounted in the distribution line along with other electrical devices. At the same time, their installed power is small and usually does not exceed 5 kW. This power is used only for heating the device, and for a stationary mode, 1/6 ... 1/9 of it is enough.
When using a steam heat exchanger or a gas burner, control and protection systems are provided, determined by the properties of energy carriers and discussed in detail above when studying the main types of thermal equipment for thermal cooking.
When comparing the designs of various thermostating apparatuses, the following considerations are usually taken into account: the lower the specific heat consumption per unit of stored products, the more efficient the hot food storage apparatus. Another important indicator that indirectly characterizes the degree of perfection of the thermostatic apparatus is the cooling rate of the product with the heaters turned off, measured in degrees per second (in K/s) or per hour (in K/h). The cooling rate of the product in perfect portable thermostats should not exceed 2 K / h, in mobile thermostats 10, and in stationary thermostats, food warmers and heating cabinets 15 K / h.
In some cases, characterized by short-term episodic use of a thermostatic device, they go to simplify the design with a conscious increase in both the cooling rate of the product and the specific energy consumption. This is justified because of the short duration of the entire process and, as a result, because of the low total energy costs.
The specificity of public catering enterprises lies not only in the use of modern technology and production technology, but also in its implementation in a short time according to the appropriate cultural and aesthetic level with the help of a variety of auxiliary heating and refrigeration equipment, as well as automated means of dispensing certain types of culinary products.
Food dispensing equipment unites a group of thermal devices designed to perform various operations not related to the process of thermal processing of products. It includes: heat racks used for short-term storage of hot dishes and heating plates; thermostats used to keep drinks hot; food warmers used to keep the first and second courses, sauces, various culinary products hot.
To heat and keep food hot, various types of gas and electric stoves are used.
The most common is the EPM-ZM electric food warmer stove (Fig.), Used mainly for the service sale of first courses.
Rice. Scheme of the electric stove of the food warmer EPM-ZM: a - design; 1 - body; 2 - introductory shield; 3 - switch; 4 - board; 5 - burner; b - communication wiring diagram
The main working body of the stove is a cast-iron burner, mounted on the support adjusting screws, which make it possible to combine the plane of the burner with the side surface of the body. To control the power of the burner, the stove is equipped with an introductory shield and a packet switch. In the first 20 ... 30 minutes, the stove is turned on at maximum power to warm it up. After that, the burner is switched to medium or low heat, depending on the required temperature and the amount of product being heated. The power consumption of the stove is 2.5 kW. Electrical safety is ensured by zeroing and protective shutdown (Fig.).
Rice. Electric circuit of the EPM-ZM plate: a - general circuit; E - burner; S - switch; X - terminal block; b - communication wiring diagram
To heat and keep hot first courses in large containers when they are served in self-service canteens, an electric food warmer stove EPM-5 is used (Fig.).
Rice. Scheme of the electric stove of the food warmer EPM-5: 1 - frame; 2 - introductory shield; 3 - switch; 4 - burner; 5 - table; 6 - shelf; 7 - bushing for cable entry; 8 - ground bolt
The electric stove has the form of an open counter, in the lower part of which three electric burners are installed on a metal frame. The base is a side-lined frame. In the upper part of the counter, a shelf for placing plates is fixed on brackets. There is also a table here.
The burners are switched on and off by package switches. Each burner is switched on separately to any of the three power levels.
The electrical wiring and the electric shock protection system are made in accordance with the rules for the installation of electrical installations. Starting and protective equipment is installed on the switchboard. The circuit diagram of the EPM-5 stove, the total power consumption of which is 3.75 kW, is shown in fig.
Rice. Schematic diagram of the plate EPM-5: SI, S2, S3 - packet switches; E7, E2, EZ - electric burners; X - terminal block
At specialized catering establishments with a bar (buffet) service method, for heating first and second courses in on-stove dishes, a tabletop electric stove PNEK-2 is used (Fig.).
Rice. Electric desktop stove PNEK-2: 1 - burner; 2 - lifting table; 3 - pallet; 4- switch
The stove has two burners, each of them is equipped with a switch, through which the power of the burner is turned on and stepwise controlled. The total nominal power of the burners is 2.4 kW.
For heating various culinary products, as well as for steaming meat, fish and vegetables, an electric steamer APE-1B is used (Fig.).
Rice. Electric steamer APE-1B: 1 - cap; 2 - perforated stewpan; 3 - sector tanks; 4 - non-perforated saucepans with a lid; 5 - working chambers; 6-lattices; 7- cap with holes of the level tube; 8 - steam generator; 9 - heaters; 10 - terminal panel; 11 - base; 12 - anchor bolt; 13 - drain tube; 14 - float ball; 15 - nutrient tank
The main working bodies of the apparatus are a steam generator, a nutrient tank, four retractable chambers.
The steam generator is filled with water from the supply tank through a system of communicating vessel, the constant level of which is maintained by a float valve. Three heating elements are attached to the bottom of the steam generator. Above the steam generator is the working chamber of the device, consisting of four rotary tanks. Under them, a fixed cap is fixed, connected to the base by three vertical posts and an axis, around which all the rotary containers of the chamber can rotate independently of one another. Each swivel container is equipped with a textolite handle with a spring lock that allows you to fix it in the closed position.
The principle of operation of the device is that the steam from the steam generator, rising from the bottom up, sequentially passes through all the containers of the chamber, where, in contact with the heated products, it condenses, giving them heat.
To protect the steam generator from overflowing with water in the event of a failure of the float valve, the steam generator is provided with a level tube through which excess water is drained into the sewer.
On fig. a diagram of the connection of communications to the device with the necessary mounting dimensions is given.
Rice. Scheme of connecting communications to a thermal apparatus of the APE type: 1 - pipeline for supplying cold water; 2 - supply and exhaust ventilation box; 3 - valve; 4 - ladder
For heating and keeping various drinks in a hot state (coffee, cocoa, milk, etc.), electric thermostats LSB-6M, ET-20, TE-25 are used. They are usually installed on buffet counters, cafeteria counters and self-service lines.
On fig. the structural diagram of the LSB-6M electric thermostat is shown.
Rice. Electric thermostat LSB-6M: 1 - tank; 2 - ten; 3 - body; 4 - crane; 5 - pallet
It is a steel cylindrical tank, turning into a rectangular flange. Heating of drinks is carried out by heating elements installed in its lower part. The thermostat is connected to the mains by means of a cord with a plug equipped with a grounding contact. The required temperature of the drink poured into the electric thermostat is maintained by the electric heater toggle switch. Tank capacity is 20 l, power consumption is 0.4 kW. Drinks are poured with the help of a splash.
The principle of operation of the electric thermostat ET-20, like that of LSB-6M. The difference lies in the fact that the drink is heated in it by a tubular electric heater located at the bottom of the tank.
Thermostat TE-25 has a removable retractable container with a tap. Its heating is carried out by analogy with LSB-6M.
The temperature control of the thermostat is carried out by a temperature sensor-relay, the dial of which is displayed on the control panel. The thermostat is equipped with a lamp signaling the inclusion of the electric heater. The useful capacity of the tank is 25 liters, the power consumption is 0.5 kW.
The main quality criterion is the product sales temperature, which varies within 60…85 °С. At these temperatures, the main biochemical processes associated with heating continue even with the preservation of products, resulting in changes that cause additional weight loss, destruction of vitamins and deterioration of organoleptic indicators.
For these changes to be minimal, the following basic requirements must be met:
The temperature of storage and implementation should have the lowest of the allowable levels;
The period of storage and sale should not exceed the allowable period and be reduced as much as possible.
Classification of hot food preservation equipment
According to the functional purpose, they are divided into three groups:
Apparatus for storing food in a hot state;
Apparatus for the sale of food;
Devices that combine the above functions and are capable of transporting hot food from a place of storage or preparation to a distribution area.
Also, products can be stored in devices designed for heat treatment: digesters, steam chambers, etc. To do this, use the lower stages of thermal power. However, from an energy point of view, this is inefficient and economically impractical.
Food warmers.
These are thermal devices designed for short-term storage of food in a hot state during its sale or in the process of manufacturing culinary products.
The design feature of food warmers is that culinary products are placed in on-stove dishes or in functional containers (gastronorms), or in special food warmers. Bain-maries of floor and desktop execution are issued.
The containers used in food warmers (bain-marie) are not thermally insulated and can be separated from the food warmer and used not only for storing finished products, but also for its preparation.
Food warmers intended for the sale of products are installed in the distribution line and are, as a rule, sectional modular devices. Such food warmers are subdivided into food warmers for second and first courses.
Bain-marie for second courses.
Depending on the method of heating, food warmers for second courses are divided into water, steam and air ("dry").
Water food warmers for second courses.
In water bain-marie as part of the distribution lines, the bain-marie is immersed in a bath of hot water. The bathtub settles down under a working surface of a table of a food warmer. Water heating in the bath is carried out either by water heating elements located inside the bath, or by air heating elements fixed on the outer side of the bath wall. Thermal insulation is usually absent, and its role is played by an air gap between the heating bath and the front panels. The temperature of the heating water in the bath is maintained by a thermostat. The temperature sensor is most often placed directly in the water. Accurately ensuring the optimum storage temperature guarantees high quality food.
Flaws: a large mass of heating water leads to an increase in the duration of heating and, accordingly, an increased energy consumption. In the process of selling products, the food-bath tanks become lighter and can float, which leads to a change in the water level in the heating bath. Heating of food warmers with different degrees of filling may be different.
Steam food warmers for second courses.
A steam generator is located in the lower part of the heating bath to heat the food processors. In this case, the heating of the food warmers is the same with different fillings. The food warmer heats up quickly and does not require a lot of energy.
Flaws. During storage, there is a danger of overheating of culinary products and deterioration of their quality, since the steam temperature, close to 100 ° C, is not regulated.
Air food warmers for second courses.
Their design differs little from steam counterparts. Air heaters are used to heat the air in the heating bath. They are placed either on the outside of the bath and pressed against its wall with brackets, or directly in the bath under the food warmers. To control the temperature, a temperature controller with a control range of up to 100 °C is used. Such food warmers quickly heat up and reach the operating mode, they are easy to use.
Bain-marie for first courses
They can be attributed to specialized "bain-marie" plates. These are devices in which food is heated using electric or gas burners. In contrast to stoves in food warmers for first courses, burners with reduced power are used, round or rectangular with a cast-iron body with a power of up to 2 kW. They are connected to the network through packet power switches.
Thermal windows.
Thermal showcases are closed chambers with shelves for laid out portioned products. The walls of the chambers are transparent: glass or plexiglass. Heating is carried out either by air heating elements or by a fan heater. In the volume, with the help of a thermostat, the temperature necessary for storing food is maintained within the range of 40 ... 70 ° C.
Heat racks.
Unlike showcases, they have open heating surfaces. Dishes are heated by heated surfaces of the production table or shelves included in the design of the apparatus.
Heating surfaces are solid or local (burner) and have a working temperature in the range of 60...85 °C.
In heat racks with a continuous heating surface in electrical design, air heating elements attached to the heating wall are used to heat it. In devices with local heating, cast-iron burners with reduced power are most often used.
Known designs of heat racks, in which a box-shaped flow heat exchanger is used as a heater, inside which an intermediate heat carrier circulates.
IK - heaters.
Outwardly similar to a table lamp lighting. The thermal block includes IK - generators and a reflector. Quartz emitters or radiating heating elements are most often used as sources of IR energy. Infrared heaters are produced as separate desktop devices or are included in the design of thermal racks, located above the working surface of the table or shelves.
Thermal cabinets.
Heating cabinets are a simplified version of ovens. The main structural element is a box-shaped working chamber, in the lower part of which heating elements are placed. Unlike ovens, they do not have the upper group of heating elements and have a thermostat with control limits of 30 ... 100 ° C.
The heating air in the working chamber is heated by natural air convection.
Heat cabinets can be built into the main technological apparatus (hot cabinet, stove or heat rack), sometimes they are completely devoid of heating.
The most effective are heated cabinets with forced air circulation, which are designed to preserve the products of the cook under the condition of forced movement of heating air and controlled humidification. In the box-shaped heat-insulated working chamber of these cabinets, the food product is placed on baking sheets. To "mix" the air in the chamber, a centrifugal fan impeller is installed. Such cabinets of the Vineton series were the first to offer the Finnish company Metos.
Optimal values of humidity and air temperature exclude drying of the product, retain the original structure and original composition, and, consequently, organoleptic properties during long-term storage.
Thermostats.
Thermostats are designed for long-term preservation and transportation of first courses and hot drinks at a constant temperature.
Their distinguishing feature is that the working chamber is an integral and completely thermally insulated part of the entire apparatus. Directly in this chamber is food intended for storage.
The main part of the thermostat is a cylindrical or box-shaped working chamber, tightly closed from above with a lid. To seal the lid, a gasket made of heat-resistant food-grade rubber is used, and to press it, special mechanical devices, often screw or cam, are used.
Depending on the capacity and method of transportation, thermostats are divided into portable, mobile and stationary.
portable thermostats are designed not only for storing and transporting hot food within the enterprise, but also for transporting it in transport.
Mobile thermostats are used for intrashop movements.
Stationary thermostats are usually installed in the line of assembly and sale of finished products.
Processes arising from the boiling of liquids. Technological aspects of use and classification of water heating equipment.
Designs and principle of operation of water heaters and boilers.
Safety regulations.
Questions for self-examination.
157. Give a picture of a bulk boiler type KNE-50, explain its device.
158. Give a diagram of the device of a continuous electric boiler of the KNE type, explain the principle of operation.
159. Give a picture, explain the device, principle of operation, technical characteristics of electric boilers of the KNE-25 type.
160. Give a picture of a universal gas boiler-water heater type KNG-200, describe its design and principle of operation.
161. Draw a diagram, describe the device and operating rules of a solid fuel (fire) boiler type KNT-200.
162. Give a drawing of a water heater type NE-1A and NE-1B, describe the device and the principle of operation.
163. Give a picture of a water heater type AGV-80, describe the device and the principle of operation.
Topic 12. Universal equipment. Auxiliary equipment and equipment for keeping food hot.
Types of universal equipment for thermal processing of foodstuffs.
Methods of heat treatment and their differences. Microwave devices, classification, design features, principle of operation.
Types of food keepers. Apparatus for keeping food hot. Classification, designs and applications.
Apparatus for peeling potatoes and vegetables. The possibility of using them in production lines for processing potatoes.
Questions for self-examination.
164. Give a classification of devices for heat treatment of products in the microwave field.
165. Give a picture of a high-frequency microwave cabinet "Electronics", describe its device.
166. Describe the device of the microwave generator (electric heaters of the third type). Give a drawing of the design of the magnetron.
167. Give a picture and describe the device of the MSESM-3K type food warmer.
168. Give a picture of food warmers for second courses of the type MSESM-60 and MSESM-110, describe their device.
169. Give a picture of a stationary electrical type ITU-84 food warmer, describe the device and the principle of operation.
170. Give a picture, describe the purpose and device of the food warmer of the mobile type MP-28.
171. Draw a picture of a mobile thermal cabinet ShTPE-1.5 and describe the arrangement of thermal cabinets such as ShTPE-1, ShTE-1, ShTE-1-01.
172. Describe the purpose, device and principle of operation of functional containers.
173. Give a picture, describe the purpose and arrangement of the distributing rack type SRTESM.
174. Describe the purpose and features of mechanized self-service distribution lines, their principle of operation, and also provide a picture of mobile food warmers of the MEP type.
175. Classification of electric food warmers for short-term storage of dishes.
176. Describe the purpose, specifications and features of self-service lines.
